System of electrical distribution.



No. 652,I87. Patented Iune.I9, |900. S. KROHN.

SYSTEM 0F ELECTRICAL DISTRIBUTION.

(Application filed Nov. 2, 1899.)

(No Model.)

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UNITED STATES lltTENT OEEIcE.

`SIGVALI) KROHN, OF BERLIN, GERMANY.

SYSTEM OF ELECTRICAL DISTRIBUTION.

SPECIFICATION forming' part Of .Letters Patent 652,187, dated June 19,1900.

DDCMBOII filed November 2, 1899. Serial No. 735,561. (N0 model- T0 a/ZZwhom, t may concern.-

' Be it known that I, SIGVALD KRQHN, a subject of the King of Sweden andNorway, residingat Berlin, Germany, have invented certain new and usefulImprovementsin Systems of Electrical Distribution, (Case No. 1,26S,) ofwhich the following is a specification.

This invention relates to electric circuits in which the earth forms aportion of the circuit, and particularly to electric-railway circuits,where the rails form part of the returncircuit. In such systems varyingdiiferences of potential exist at dierent points of the rail-circuitboth by reason of the inherent resistance of the rail or earth returnbranch and by reason of the varyingload imposed by liuctuations oftraffic. Such dierences of potential tend to develop stray currents,ordinarily called earth-currents, spreading outwardly from the conductorthrough the earth in a loop, connecting points of different potentialand creating considerable annoyance. These currents not only affectother conductors traversing the neighborhood of the points of differentpotential, but corrode pipes or other metallic bodies buried in theearth in the path of the disturbance. My invention provides for areduction of the differences of potential at different part-s of thereturn-circuit and is carried out by the interposition of acounter-electromotive-force device between the station end of the railbranch and the generator and an auxiliary feeder connected from theground side of the generator to the rail branch at a point or pointsdistant from the station where the difference of potential may besufficiently greater than that at the station end to cause trouble fromthe causes above noted. A satisfactory type of suchcounter-electromotiveforce device may be an electric motor, which beinginterposed in the return-circuit will vary in speed with the load of thesection it protects. This motor may be employed to drive an auxiliarygenerator or booster to raise the potential in the positive feeder ofthe section protected, thereby promoting a greater economy in theoperation of the system of distribution. The best resultsare obtainedwhen the counter electromotive force of the motor plus its O2R lossequals the CR loss of the negative feeder, connecting the distant partof the track-circuit with the generator. The motor should be separatelyexcited to render its speed directly variable with the load on thesystem, so that if a heavy current return through a negative feeder themotor will draw a correspondingly-heavy current and generate a counterelectromotive force about equal to the drop in the feeder, and,inversely, if a small current be flowing in theA feeder a small currentwill be drawn by the motor, and a small drop in the feeder will becounterbalanced by the small counter electromotive force of the motor.The action of the motor lowers the difference of potential between thepoints of the track included in its circuit, and thus cuts down thestray currents through the earth. The generator should not be directlygrounded at the station.

The features of novelty of my invention will be more specificallydescribed hereinafter and will be definitely indicated in the claims.

In the accompanying drawings,which illustrate my invention, Figure l isa diagram of a system wherein a simple counter-electromotive-forcedevice, such as a motor, is einployed to counteract earth-currents. Fig.2 is a diagram of a system in which the power developed by this motor isemployed to operate a booster feeding the positive side of the system.Fig. 3 is a similar organization in which the generating-station isequipped with a storage battery for economizing power.

Referring first to Fig. 1, l represents a generator located at asupply-station and furnishing power for a circuit, including a railbranch 2. 3 represents an overhead trolleywire or other insulatedconductor leading from the station to the points along the line to whichcurrent is to be delivered, and 4 represents part of the load, such as atrolley-car or other shifting load on the system. The differences ofpotential in the rail branch 2 at different points thereof depend on itsresistance and on variations of load and changes of position of thecars. The resistance of the conductor is a fixed conditiomdependin gupon the installation; but in all cases where no provision is made toguard against it sufficient difference of potential exists betweenterminal points of a track-section, such as 2, and the earth to setupearth-currents in the neigh IOO -the generator, as indicated at 6.

.positive feeder of the'control-station.

borhood. The value of these differences of potential depends upon thedrop over the return branch 2. I intel-pose a source of counterelectromotive force 5 between the end of the track-section nearest thestation and the generator and connect an auxiliary feeder, which may bestyled a negative feeder, between the remote end of the track-sectionand This motor absorbs part of the drop over the return branch, andthereby lowers the drop between the terminals of the section 2, and itscounter electromotive force tends further to equaliZe the potential atthe terminals of the railsection 2. The best conditions are obtainedwith a separately-excited field for the motor, so adjusted as to enablethe counter electromotive force to balance the drop of voltage in thenegative feeder 6. A separate negative feeder and motor, such as 6, maybe employed for each track-section of the system.

In the organization shown in Figs. 2 and 3 the energy developed by themotor is employed to raise the potential of the positive feeder leadingto the same point of the line as the negative one which connects withthe motor. The motor may be belted or otherwise mechanically connectedwith an auxiliary generator or booster '7, which isinterposed in seriesrelation between the generator and the In Fig. 3 a similar organizationis shown in a system where a storage battery in shunt to the generatoris used to more economically operate the station. In theseorganizations, where the positive feeder leads to the same point of theline as the negative one, the current in both is about the same, andtherefore the booster, which for the best results should be providedwith a separately-excited field, always gives the motor a proper loadand economizes the operation of the system, at the same time generatingpotential proportiontial to the drop in the feeder in which it isconnected.

Vhat I claim as new, and desire to secure by Letters Patent of theUnited States, is-

1. The combination with an electric circuit having an earth-return, ofmeans for preventing stray earth-currents, comprising acounter-electromotive-force device between the low-potential end of theearth branch and the generator.

2. The combination with an electric circuit having an earth-return, ofmeans for preventing stray earth-currents comprising a source ofopposing electromotive force in the circuit at the low-potential end ofthe earth branch to raise its potential.

3. In a system of electrical distribution having a partial earthedcircuit, means for preventing stray earth-currents between differentparts of the earth branch, comprising a counter-electromotive-forcedevice between the low-potential end of said branch and thesupply-generator and a feeder leading to a point of higher potential inthe earth branch.

et. In a system of electrical distribution having a partial earthedcircuit, means for preventing stray earth-currents between differentparts of the earth branch comprising an electric motor between alow-potential point of the earth branch and the generator, and a feederleading to a point of higher potential.

5. In asystem ofy electrical distribution having a partial earthedcircuit, means for preventing stray earth-currents between differentparts vof the earth branch, comprising an electric motor in thereturn-circuit, and a booster driven by said motor to supply a feedwire.

6. In a system of electrical distribution having a partial earthedcircuit, means for equalizing the potential on the earthed conductor,comprising an electric motor in the returncircuit at a low-potentialpoint, a negative feeder connecting the generator with a point of higherpotential, and a booster in a positive feeder operated by the motor.

7. In a system of electrical distribution having a partial earthedcircuit, means for reducing the drop in the feeders, comprising anelectric motor in the earthed branch at a point of relatively-lowpotential, a negative feeder connecting the generator with a point ofhigher potential, a booster operated by the motor and connected to apositive feeder for la point of the system corresponding to the point ofhigh potential of the earthed branch. In witness whereof I have hereuntoset my hand this 16th day of October, 1899.

SIGVALD KROHN.

IOO

